This application claims the priority of Korean Patent Application No. 2003-2381 filed on Jan. 14, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device having a backlight apparatus.
2. Description of the Related Art
FIG. 1 is a sectional view illustrating a conventional liquid crystal display device. Referring to FIG. 1, a liquid crystal display device includes a liquid crystal panel 10 and a backlight apparatus 30. The liquid crystal panel 10 is manufactured by sequentially depositing a lower substrate 1, a lower electrode 2, a liquid crystal layer 3, an upper electrode 4, and an upper substrate 5. Polarization panels 6 and 7 are further provided at a lower surface of the lower substrate 1 and an upper surface of the upper substrate 5, respectively. The liquid crystal panel 10 displays a desired image by changing orientation of liquid crystal molecules in the liquid crystal layer 3 according to an electric signal applied to the lower and upper electrodes 2 and 4 so as to transmit or block light input from the backlight apparatus 30.
The backlight apparatus 30 is an illumination apparatus for supplying light to the liquid crystal panel 10. The backlight apparatus 30 includes a light guide panel 12, a dispersion pattern 18, a reflection panel 11, and a light source 13. An optical film layer 20 is deposited on an upper surface of the light guide panel 12. The light emitted from the light source 13 is incident on a side surface of the light guide panel 12. The light guide panel 12 is a transmissive body having a refractive index of about 1.5, in which a critical angle is about 42°. Thus, of the light incident on the light guide panel 12, the light having an incident angle less than a critical angle with respect to the upper surface of the light guide panel 12 is exhausted through the upper surface of the light guide panel 12 and the remaining light is totally reflected and spreads in the entire area of the light guide panel 12. The dispersion pattern 18 is provided on a lower surface of the light guide panel 12. The dispersion pattern 18 disperses light and, as shown in FIG. 1, some of the dispersed light proceeds toward the upper surface of the light guide panel 12 and the light passing through the dispersion pattern 18 is reflected by the reflection panel 11 to proceed upward. Of the light proceeding upward, the light having an incident angle with respect to the upper surface of the light guide panel 12 that is less than a critical angle is transmitted, while the remaining light is totally reflected again and spreads inside the light guide panel 12. By repeating transmission, total reflection, and dispersion, the backlight 30 functions as a surface light source for supplying light to the liquid crystal panel 10.
The light passing through the upper surface of the light guide panel 12 is incident on the liquid crystal panel 10 via the optical film layer 20. The optical film layer 20 can include a diffusion panel 14, prism sheets 15 and 16, and a protector 17. The diffusion panel 14 makes the strength of the light exhausted from the upper surface of the light guide panel 12 uniform by diffusing the light. The prism sheets 15 and 16 improve brightness in a normal direction.
In the above-described liquid crystal display device, loss of light is generated as the light emitted from the light source is absorbed by a plurality of optical media such as the light guide panel and the optical film while the light passes through the respective media and arrives at the liquid crystal panel. Thus, a high power light source is needed to obtain a desired brightness from the liquid crystal panel. However, the high power light source normally has a large size and a great power consumption. Furthermore, since the thickness of the light guide panel is about 2–3 mm, there is a limit to making a thin liquid crystal display panel with a backlight apparatus using the light guide panel.